The catching of criminals and finding other persons of interest can be difficult in modern circumstances. Unless a perpetrator is apprehended at the scene of a crime in front of witnesses, for example, he or she can quickly become hard to identify and even harder to find. Two factors contributing to this difficulty are population density and mobility. With so many people living in a relatively small geographic area, a person who commits a crime can quickly blend into the general population and almost disappear. In addition, the ability of one person to move quickly from one place to another—even a distant—location has increased dramatically. As a result, the perpetrator can both flee the scene quickly and soon strike again in a different jurisdiction.
Needless to say, agencies such as local, state, and federal law enforcement can use all the assistance modern technology is able to provide. They can of course take advantage of rapid transportation themselves, but are frequently bound to stay within a single jurisdiction. Communication methods have also improved, but each agency still needs something in the way of information to communicate to another agency that will further the effort to identify, locate, and capture the wanted suspect.
One technological aid that has proven useful to law enforcement is the surveillance video camera. As video cameras have become relatively inexpensive, they have become almost ubiquitous in some locales. The technology associated with collecting and storing the captured images has also improved, so a continuous video record can be preserved for quite some time. Video cameras can even be installed in hidden and inaccessible locations, so detecting them and frustrating their operation can be a challenge. Naturally, video cameras are often placed in locations where undesirable behavior is a strong possibility, such as in back of or near the entrance to retail outlets. Many individuals also use video surveillance in their homes.
For this reason when a crime, terrorist attack, or other undesirable activity occurs, law enforcement agencies often canvass the area to determine of a video image related to the event can be found. Most useful, of course, is a video capturing the image of persons in the area at the time. If the image of any given subject is sufficient for purposes of identification, the then known whereabouts and movement of the subject can be used for the investigation. If the person identified is a known criminal, for example, an attempt may be made to see if other evidence relates them to the event in question. The identified person may even be contacted and interviewed, if possible. By the same token, the presence of an individual in the vicinity of a number of similar events might raise suspicion as well.
Unfortunately, video surveillance as an enforcement tool has its limitations. Even where there are many cameras, they each have a limited field of vision and can only capture so much. Frequently, cameras are deployed to cover a specific area and even people passing by this area are recorded imperfectly. Even when in view, a person may be turned the wrong way or wearing, for example, a hat and dark glasses that make identification difficult if not impossible. Many criminals, of course, dress themselves in such a manner so as to purposely make it hard for an eyewitness—either live or by videotape—to later identify them. Another obstacle may be the sheer volume of video evidence that may be available. Hours of video may have to be viewed in order to make even a small amount of progress in an investigation. While some automated recognition techniques may be used, these also suffer from the disabilities associated with incomplete images and intentional efforts to frustrate witnesses.
There is a continuing need, therefore, for a way to investigate which persons might have been present at or near the scene of an event to determine whether their activities might be considered suspect.